Plastics films of this type form shrink-label base films or shrink-label backing films, these labels being applied by shrinkage onto cylindrical batteries, such as dry-cell batteries. In that process, shrink labels have to be capable of application via heating and shrinkage to appropriate size for a prescribed final configuration, corresponding to the periphery and the face sides of the cylindrical batteries. This shrinkage force arising here has to be withstood by the adhesive with which the shrink label is applied along the periphery.
These base films or backing films are subject to stringent requirements in relation to shrinkage properties, appearance, layflat, number of holes, printability, and minimization of surface defects.
The prior art discloses shrinkable PVC films of U.S. Pat. No. 4,911,994, corresponding to German patent DE 34 30 162 C2 and to German patent 33 22 309 C3.
For example, German patent 33 22 309 C3 describes a multilayer adhesive-bondable sleeve label which can be applied by adhesive bonding and shrinking onto a peripheral surface of a body of a dry-cell battery, and which has a backing having a reverse side with a pressure-sensitive adhesive layer, there being a protective layer on the upper side of the backing. The backing comprises at least one shrinkable plastics film composed of rigid polyvinyl chloride and stretched in the circumferential direction of the body. The protective layer is composed of a shrinkable transparent protective covering film stretched in the circumferential direction of the body. A print has been applied to that side of the backing which faces away from the protective covering film. The protective covering film has been applied to the print by means of a laminating adhesive layer. A layer of material visible through the protective covering film has been vapor-deposited onto the plastics film. Marginal regions of the protective covering film protrude over both margins of the backing in the axial direction of the peripheral surface of the body.
EP-B 0 176 704 describes a shrink label of similar structure in which there is at least one stamped cut in the backing, in the vicinity of its edge extending along a line enveloping the peripheral surface of the body. Once the shrink label has been applied by shrinkage, the edge covers the edge which is parallel thereto.
None of the documents mentioned discloses an extent for the change in the dimension of a plastics film composed of PVC as a result of application by shrinkage onto a cylindrical body.
EP-B1 0 578 750 describes shrink labels composed of polypropylene, where the polypropylene film can undergo heat shrinkage in one dimension by 20% or more at elevated temperatures. The initial shrinkage factor is from 20 to 50% at temperatures in the range from 116 to 138° C. Polypropylene is accompanied by various problems, for example during the printing of markings, during the vapor-deposition of metal layers, and during the application of adhesives. Specific treatments are required to make the abovementioned materials adhere to polypropylene. This makes the production of sleeve labels more expensive than that of PVC-based labels. For example, corona treatment is required for the metallizing of one side of the polypropylene, while the other side of the polypropylene, the side to which the adhesive is applied, also has to be corona-treated, but the corona power used for this is different from that for the corona treatment for the metallization. Priming or surface coating is needed for the printing of polypropylene.
These problems are of substantially smaller magnitude when use is made of plastics films composed of polyvinyl chloride, rather than polypropylene.
It is an object of the invention to provide a calendered plastics film composed of polyvinyl chloride for shrink labels of the type described at the outset, which undergoes a large change in its longitudinal dimension during heat shrinkage.
For the purposes of this object, the change in dimension in the transverse direction during heat shrinkage of the plastics film is to be very small.
The invention achieves this object in that the plastics film has been stretched in the machine direction of a calender and has a positive heat shrinkage of from 40 to 60%.